June 17, 2021

For Your Enjoyment, a Home Run Rate Refresher (FanGraphs)


Here’s a question for you: does Mike Trout hit more home runs against bad pitchers? The answer is yes, of course, but we can parse the question a little differently to make it more interesting. How about this one: does Mike Trout hit more home runs per fly ball against pitchers who are home run-prone? That at least has some intrigue.

Here’s one way you might do this study. Take every pitcher in baseball and group them into quartiles based on their home run per fly ball rate. I’m using line drives and non-pop-up fly balls to make a slightly different rate, but the idea is the same. With the pitchers bucketed like so, simply observe Trout’s home run rate against each quartile:

Mike Trout Versus

Stat Quartile 1 Quartile 2 Quartile 3 Quartile 4
HR/Air% 13.33% 16.44% 26.76% 20.00%
Batted Balls 45 73 71 30

But before Tom Tango pulls his hair out, let me add something important: This is a bad way to do this study. There’s a big problem here. Trout’s home runs and the pitchers’ home run rate aren’t independent of each other. If Trout tags a guy for a few home runs, that pitcher’s home run rate goes up. If Trout doesn’t hit any out against a pitcher, that…

Read “For Your Enjoyment, a Home Run Rate Refresher” at FanGraphs